Stress often has detrimental effects on memory and cognition, effects that are especially challenging for older adults to sustain on top of existing age-related declines. In this project, we investigate whether estradiol (E2) protects against such effects. In humans E2 reduces the magnitude of the stress response and aids cognition. Further, in vitro and in vivo animal research shows that E2 protects the brain from the negative effects of stress hormones. Together, this pattern of results suggests the E2 may protect aging women's neural and cognitive integrity during times of stress. The current application tests this hypothesis by examining the effects of short-term E2 treatment on various systems affected by stress as well as testing a mechanism of action for E2 protection. First, we will examine the ability of a short-term E2 intervention to reduce physiological effects of stress, stress-induced impairments in working memory performance, and associated changes in brain activation. Work in our laboratory reveals that post-menopausal women with high salivary E2 levels as a result of taking E2 supplements release less of the stress hormone, cortisol, in response to a stressor than women with low salivary E2 levels. We also found that working memory performance in the high-E2 women was unhindered by stress, whereas low-E2 women performed significantly worse under stress than under control conditions. As a result of the E2-related reduction in stress hormone release we expect to find that E2 will be associated with 1) dampening the stress-induced changes in hippocampal cerebral blood flow and bilateral connectivity at rest during stress and control conditions, 2) smaller stress-induced decreases in heart-rate variability, and 3) hippocampal and prefrontal cortex activity while playing a working memory game. Second, we will test a potential mechanism of action for estradiol protection against stress. We hypothesize E2 limits vulnerability of the hippocampus to the effects of stress, allowing the hippocampus to effectively shut down the stress response, which curtails the levels of cortisol available and the amount of time cortisol is available to act on neural tissue. To test this we will compare estradiol and placebo groups on hippocampal cerebral blood flow and bilateral functional connectivity at rest, under stress and control conditions. These measures will be correlated with all estradiol levels, cortisol response, HRV, and working- memory-related brain activity and performance. The proposed research aims to uncover whether E2 can in fact reduce the negative effect of stress on memory in post-menopausal human females, as well as the brain mechanisms involved in this protection against stress. This research will further inform the medical field on the effects of E2 on stress and memory, which could lead to better guidance and advice for patients seeking information on E2 treatment during or after menopause.